1. Field
The exemplary embodiments relate to a substrate transport apparatus and, more particularly, to a substrate transport apparatus with an articulated arm.
2. Brief Description of Related Developments
Contemporary SCARA arm robots used for transporting substrate have equal length links (i.e. upper arm and forearm). When the upper arm and forearm are of the same length the SCARA arm has a limited containment to extension ratio, the containment reflecting the footprint (generally commensurate to the swing diameter of the retracted arm) of the robot and the extension being the maximum reach of the robot arm. In conventional arms, to enable greater extension of a robot with equal length links the links of the robot are increased in length by the same amount. In conventional arms, the end effector rotation will track with the rotation of the upper arm. The end effector remains parallel to and along the axis of radial extension of the arm. Due to the increased linkage length, the swing diameter (i.e. the footprint) of the robot while in the retracted position also increases.
Various types of substrate transport apparatus are known in the art. Examples of conventional substrate transport apparatus are discussed in U.S. Pat. Nos. 5,741,113 ('113) and 5,611,655 ('655). U.S. Pat. No. '113 discusses a multiple link robot arm mechanism that uses two motors to rotate the upper arm and forearm. The motors are capable of synchronized operation to permit movement of the robot arm hand along a curvilinear path as the extension of the hand changes. The hand rotates about a wrist axis in response to rotation of the forearm about an elbow axis. U.S. Pat. No. '655 discusses a transport having a multi-joint arm with three links where each of the links are independently rotatable. The arms are driven by a drive unit having three motors. In both '113 and '655 the upper arm and forearm of the robots are equal in length. As such, longer reach of the arms in '113 and '655 means a larger footprint. In addition, at least in '113 the end effector is not orthogonal to the substrate holding area.